Evaluation of Patient Setup Errors in Pelvic Cancer Radiation Therapy: A Comparative Study Between 3D Surface Imaging (AlignRT) and Conventional Laser Alignment

Abstract

Background: Radiation therapy plays an important role in treating cancers located in the pelvic region. The patients have to be treated in multiple fractions, therefore, the accuracy of patient setup before each treatment session directly impacts the effective treatment.

Objective: To compare the setup errors in pelvic cancer patients using laser alignment system versus 3D surface imaging system (AlignRT). The study also examined the characteristics of the AlignRT system.

Materials and Methods: The study began with an evaluation of the characteristics of the AlignRT system, including daily quality assurance checks, factors that may affect system performance, and the system’s accuracy in detecting setup errors. Data were then collected from 10 pelvic cancer patients positioned using a laser system and the AlignRT system. Position verification was performed before radiation using Cone Beam Computed Tomography.

Results: The study of AlignRT system characteristics showed that daily setup errors were within 0.4 millimeters. Factors from gantry angle, couch angle, room lighting, and region of interest were within 0.2 mm, 0.1 degrees, 0.1 mm, and 0.2 mm, respectively. Clinically, setup errors in patients positioned with the AlignRT system were smaller than those positioned with the laser system in both the longitudinal and lateral directions. A statistically significant difference was found in the lateral direction, but not in the longitudinal or vertical directions.

Conclusion: The AlignRT system demonstrates high accuracy and precision, and it can be effectively applied for pre-radiation positioning in pelvic cancer patients, serving as a viable alternative to traditional methods such as skin marking or laser systems.